Cell search/detection is an important procedure for a mobile device deployed in a cellular network. Typically, reference signals are used to identify a cell which needs to be detected by the mobile device during operation. Reference signals are data symbols which are known at the receiver and are used for parameter estimation tasks, e.g. cell-identity (cell-ID) detection.
In a cellular network, a supplied area is split into cells, each cell being equipped with a base station which serves the mobile stations in that cell. Each cell needs to be uniquely identified if a mobile devices wishes to connect to a cell or if the mobile device is already connected to a cell and wishes to connect to another cell. For this purpose a base station transmits a cell identity (cell-ID) within the Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS). There are 504 unique physical layer cell identities in LTE, grouped into 168 groups of three identities. Three PSS sequences are used to indicate the cell identity within the group and 168 SSS sequences are used to indicate the identity of the group.
In the mobile device, in order to enable reliable data reception, a number of parameter estimation tasks need to be performed, e.g., time synchronization estimation, frequency synchronization estimation, channel estimation, interference level estimation, Doppler spread estimation, power delay profile estimation, feedback information estimation. PSS detection is used for slot timing detection and physical layer ID detection. SSS detection is used for radio frame detection, cyclic prefix (CP) length detection and TDD/FDD detection. SSS detection is based on coherent demodulation in frequency domain.
Present solutions employ oversampling during reference signal detection, for example 2× oversampling during PSS detection and SSS detection in order to achieve good cell search sensitivity.
There are some obvious draw backs associated with 2× oversampling rate processing. With 2× data to be processed, more dynamic power is consumed at silicon side. Moreover, much more hardware resources are required with 2× data, leading to more hardware cost and more leakage power. This is especially true for memory requirement, which usually is the dominant part for hardware cost in cell searcher design.
Hence, what is needed is a solution for cell searching having low memory requirement.